Photonic analog to digital conversion (PADC) techniques have been progressing rapidly in recent years, and have become hotspots in photonic electronics. Since PADC performance depends on properties of the photonic sampler thereof, how to generate a high-speed and stable optical pulse sequence for the photonic sampler has become an important subject in the field of the art. Time-wavelength interleaved technique (Clark T R, Kang J U, Esman R D, Performance of a time-wavelength interleaved photonic sampler for analog-digital conversion [J]. Photonics Technology Letters, IEEE, 1999, 11(9): 1168-1170.), as an effective method for generating an ultra-high repetition rate optical pulse sequence, makes full use of low jitter property of a mode-locked laser and advantages of the high repetition rate and wide band thereof to generate a stable ultra-high speed optical pulse sequence, thus becoming a general method for generating an ultra-high speed photonic sampling clock.
However, for an ultra-high speed photonic sampling clock generated by time-wavelength interleaving, there exist some extent mismatches among different channels in respect of time delay, amplitude and pulse shapes. In actual scenario, variable optical delay lines and a variable attenuator are introduced in each channel for adjustment of mismatch of time delay and amplitude (Zou, Weiwen; Li, Xing, et al., An ultra-high speed photonic digital to analog conversion method and device therefor, China Patent No. 201410065510.7 [P], 2014). For compensation of channel mismatch, real time measurement of the pulse sequence in each channel is needed by means of experiment, and the variable optical delay lines and variable attenuators are adjusted in accordance with the measured amplitude and delay information for realization of matching among the channels. For comparative low repetition rate optical pulse sequences, amplitude and time delay information may be obtained simply by means of time-domain observation via an oscilloscope. However, for ultra-high speed optical pulse sequences, time-domain measurement thereof cannot be implemented due to limitation of sampling rate of the oscilloscope. Therefore, other methods are needed to be sought out for measurement of channel mismatch of an ultra-high speed time-wavelength interleaved optical pulse sequence.